自学C语言中相关知识，设计出模拟简单计算器程序。要求如下所述：
1．　　.必须具有+、－、×、÷简单算术运算以及清除的功能
2．　　输出显示简易计算器的界面；
3．　　可以通过键盘上“↑←↓→”符号来选择需要输入的数据，点击键盘上“＝”或者计算器界面的“＝”将计算结果输出显示；
4．　　也可以通过输入窗口，直接从键盘上输入要计算的表达式，点击键盘上“＝”或者计算器界面的“＝”将计算结果输出显示；
5．　　选用任意一种（上述3或4）数据输入方法的测试表达式及运算结果均可以完整地在某个窗口中显示出来。
6．　　可以自行添加额外功能（选做，可加分）。(Self learning C language related knowledge, designed to simulate a simple calculator program. The following are required:
1.. We must have simple arithmetic operations and elimination functions.
The 2. output shows the interface of the simple calculator.
3. can select the data that needs to be input by the keyboard on the keyboard, click "=" on the keyboard or the "=" of the calculator interface to display the result of the calculation.
4. can also enter through the input window, direct input from the keyboard to calculate the expression, click "=" on the keyboard or the "=" of the calculator interface to display the results of the calculation;
5. the test expression and result of any one (3 or 4) data input method can be displayed in a certain window.
6. you can add additional functions by yourself.)